JP2006159586A - Multi-beam image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-beam image forming apparatus which forms an image of a good image quality by matching an image formation starting position of each laser beam at the time of simultaneously recording image data of a plurality of lines by using a plurality of the laser beams, and also which prevents an effective scanning range from being narrow. <P>SOLUTION: The multi-beam image forming apparatus has a multi-beam generating means for generating 2n laser beams by synthesizing the laser beams generated by a first and a second semiconductor laser arrays, and a beam detecting means for generating a synchronization detection signal so as to synchronize scanning of the laser beams. The beam detecting means is constituted of a first and a second beam detecting beams arranged at almost the same position in a main scanning direction of the laser beams, and side by side in a sub scanning direction. The image formation starting position by the multi beams is controlled on the basis of the detection signals from the first and the second beam detecting means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using a multi-beam scanning device that simultaneously scans multiple beams, and more particularly to a multi-beam capable of obtaining a good image quality by aligning image formation start positions even when a large number of beams are used. The present invention relates to an image forming apparatus.

  In an electrophotographic apparatus such as a laser printer or a digital copying machine, a photosensitive drum is uniformly charged, and then an electrostatic latent image corresponding to recorded information is formed by an exposure apparatus using a laser beam. The image is developed with toner, transferred to a sheet at a transfer portion, and further fixed to form an image on the sheet.

  Conventionally, as this type of image forming apparatus, a multi-beam image forming apparatus including a multi-beam scanning apparatus that simultaneously scans a plurality of lines by scanning a plurality of laser beams with a polygon mirror has been proposed. Since such a multi-beam image forming apparatus forms a plurality of lines of images on one surface of a polygon mirror, it has a feature that high-speed image formation can be performed using a low-speed rotating polygon motor and a low-power semiconductor laser.

  In a multi-beam image forming apparatus, in order to simultaneously record image data for a plurality of lines using a plurality of laser beams, it is necessary to align the image formation start positions of the respective laser beams. Indispensable. Therefore, generally, before starting image formation, a laser beam is irradiated to a beam detecting means arranged at a predetermined position outside the effective scanning range, and control is performed with a predetermined time interval from the beam detection signal as an image formation start position. The method is used.

  For example, when a plurality of laser beams are aligned in the main scanning direction, one laser beam is emitted from the plurality of laser beams and irradiated to one beam detection unit, similarly to an image forming apparatus that uses one laser beam. The image formation start positions of all the laser beams can be controlled by the beam detection signal. However, such a method has a limit in terms of increasing the accuracy of the synthesis of a plurality of laser beams, and even if it can be synthesized with a high accuracy, the accuracy of the synthesis can be reduced due to environmental changes and vibrations. It is inevitable that it will deteriorate over time. Therefore, it is difficult to always stably align the image start positions in the main scanning direction by the laser beams.

  In order to solve such problems, Patent Document 1 (Japanese Patent Laid-Open No. 10-202943) discloses a method of controlling the image formation start position of each of a plurality of laser beams.

  FIG. 13 is a schematic diagram showing a part of the image forming apparatus for explaining the above method. 1 is a polygon mirror, 2 is an imaging lens system, 3 is a mirror, 4 is a photosensitive drum, and 5 is synchronous detection. Reference numeral 6 denotes a laser control unit.

  LD1 and LD2 are first and second semiconductor laser light sources. The laser beams from the two light sources LD1 and LD2 are reflected by the deflecting and reflecting surfaces of the polygon mirror 1 and are shaken in the horizontal direction, and then an fθ lens or the like. Focusing light is generated by the imaging lens system 2. Further, the optical path is bent downward by the mirror 3 and condensed as two light spots S1 and S2 on the photosensitive drum 4, and the electrostatic drum 4 is simultaneously scanned in the main scanning direction to form an electrostatic latent image.

  The first and second semiconductor laser light sources LD1 and LD2 are arranged side by side in the main scanning direction so that the light spots S1 and S2 are formed at a slight distance P corresponding to the resolution as shown in FIG. Has been. For this reason, the positions of the two light spots S1 and S2 that scan the photosensitive member 4 and the synchronization detection unit 5 are shifted by a distance L in the main scanning direction and pass through the light receiving surface 5a of the synchronization detection unit 5. A time difference corresponding to the distance L is generated.

  Accordingly, when the semiconductor laser light sources LD1 and LD2 are caused to emit light at a timing as shown in FIG. 15, the synchronization signal outputs (A) and (B) corresponding to the light spots S1 and S2 from the light receiving surface 5a of the synchronization detector 5 are illustrated. ) Is obtained. By controlling the semiconductor laser light sources LD1 and LD2 by the laser controller 6 based on the synchronization signals (A) and (B), the start position in the main scanning direction of each laser beam can always be controlled stably.

  However, in the above control method, when the semiconductor laser light sources are formed in an array and the number of laser beams is further increased, for example, when 10 laser beams are used, there is a problem that the effective scanning range becomes narrow.

  That is, as shown in FIG. 16, when the spots S1 to S10 of the ten laser beams are shifted at predetermined intervals in the main scanning direction and the sub-scanning direction, the scanning with the laser beam is expressed as shown in FIG. Since the effective scanning range of the laser beam is a range where all of the scanning lines S1 to S10 overlap, the effective scanning range is a predetermined range R1 from the image formation start position X. Therefore, it is difficult to avoid the problem that when the image is formed as shown in FIG. 16, the overlap portion is reduced and the effective scanning range is narrowed.

  On the other hand, in Patent Document 2 (Japanese Patent Laid-Open No. 6-344592), two beam detection means are arranged in the main scanning direction, the first beam detection means detects the beam of the first semiconductor laser, and the second A method of generating a synchronization signal (beam detection signal) serving as a reference for aligning image formation start positions by detecting a beam of a second semiconductor laser with a beam detection means is disclosed.

  However, this method also has a problem that since the plurality of beam detecting means are arranged side by side on the main scanning line, the scanning range for beam detection becomes long, and as a result, the effective scanning range becomes narrow.

Japanese Patent Laid-Open No. 10-202943 Japanese Patent Laid-Open No. 6-344592

  The problem to be solved by the present invention is to provide a multi-beam image forming apparatus that solves the problems of the conventional control system as described above.

  Specifically, the object of the present invention is to always stably control the image start position of each laser beam in the main scanning direction even if the synthesis accuracy of a plurality of laser beams is lowered due to a change over time, etc. An object of the present invention is to provide a multi-beam image forming apparatus in which the effective scanning range is not narrowed even if the number of laser beams is increased.

  In order to achieve the above object, the present invention provides first and second semiconductor laser arrays, and first and second semiconductor laser arrays each comprising n (n is an arbitrary integer greater than or equal to 2) laser elements. A multi-beam generating means for generating 2n laser beams by synthesizing the laser beams generated by the laser beam, a scanning means for scanning the 2n laser beams generated by the multi-beam generating means, and scanning of each laser beam. In a multi-beam image forming apparatus comprising a multi-beam scanning device having a beam detection means for generating a synchronization detection signal for synchronization, the beam detection means is positioned at substantially the same position in the main scanning direction of the laser beam. The first and second beam detectors are arranged side by side in the scanning direction, and the first semiconductor laser array is formed by the first beam detector. The n number of laser beams are detected, and the second beam detecting means performs the n laser beam detecting means for the second semiconductor laser array, and the first and second beam detections. One feature is that the image forming start position by the multi-beam is controlled based on the detection signal from the means.

  Another feature of the present invention is that the beam detecting means is composed of first and second beam detecting means arranged at a position shifted by a predetermined interval L1 in the main scanning direction of the laser beam and arranged in the sub-scanning direction. The first beam detecting means detects n laser beams of the first semiconductor laser array, and the second beam detecting means detects n laser beams of the second semiconductor laser array. The beam detection means is used to control the image forming start positions of 2n multi-beams based on the detection signals from the first and second beam detection means.

  Another feature of the present invention is that when detecting n laser beams generated from the second semiconductor laser array, the laser beam generated from the second semiconductor laser array passes over the second beam detecting means. Thus, there is provided a deflecting means for deflecting the optical path of the beam.

  Another feature of the present invention is that an optical element is inserted between the scanning means and the beam detecting means at the time of beam detection, and the optical element emits the laser beam generated by the first and second semiconductor laser arrays. The laser beam generated from the first semiconductor laser array is transformed into a shape that passes through both the first and second beam detection means. The control is to turn off the light when passing through and to turn off when the laser beam generated from the second semiconductor laser array passes through the first beam detecting means.

  According to the present invention, beam detection is performed for each of a plurality of laser beams, and the multi-beam image formation start positions can be aligned based on the detection signals, so that a high-quality image can be obtained. Further, since the two beam detection means are arranged in the sub-scanning direction at substantially the same position in the main scanning direction, the area occupied by the beam detection means in the main scanning direction can be reduced. The effective scanning range can be widened.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

Example 1
FIG. 1 is a partial schematic configuration diagram showing a first embodiment of a multi-beam image forming apparatus according to the present invention. In the figure, reference numeral 100 denotes a photosensitive drum, which is rotationally driven by a motor (not shown). The surface of the photosensitive drum 100 is uniformly charged by a charging device (not shown), and then irradiated with a laser beam according to recording information to form an electrostatic latent image. This electrostatic latent image is developed by a developing device (not shown), and further transferred to a recording paper or the like by a transfer device (not shown) to form an image.

  Reference numerals 101 and 102 denote semiconductor laser arrays (hereinafter abbreviated as LDA), which respectively generate a plurality of laser beams according to image data. The laser beam generated by the LDA 102 is reflected by the mirror 111 serving as a deflection unit, and then enters the beam splitter 103 and is combined with the laser beam emitted from the LDA 101. The plurality of combined laser beams are applied to the deflecting / reflecting surface of the polygon mirror 104 which is scanning means for scanning the surface of the photosensitive drum 100. The laser beam from the polygon mirror 104 is imaged on the photosensitive drum 100 through imaging means such as an fθ lens 105. The formed light spots of the plurality of laser beams are formed at predetermined intervals in the sub-scanning direction, and the surface of the photosensitive drum 100 is scanned at a constant speed. For example, when the resolution is 600 dpi, the image is formed on the photosensitive member with a shift of 42.3 μm in the sub-scanning direction.

  The plurality of laser beams generated from the first LDA 101 and the second LDA 102 are formed at predetermined intervals in the main scanning direction, and each m-th (m is an arbitrary integer greater than or equal to 2) -th. Are adjusted so that the positions of the laser beams in the main scanning direction are aligned, and are combined by the beam splitter 103.

  FIG. 2 shows the positional relationship of 10 laser beams (S1 to S10) imaged on the photoconductor when a 5-element (n = 5) LDA is used. In other words, in this embodiment, odd-numbered laser beams S1, S3, S5, S7, and S9 are generated by the LDA 101, and even-numbered laser beams S2, S4, S6, S8, and S10 are generated by the LDA 102, and S1, S3, S2, and Images are formed so that S4,... S9 and S10 are aligned in the main scanning direction.

  On the other hand, reference numerals 106 and 107 in FIG. 1 denote beam detection means, which are arranged at positions adjacent to the photosensitive drum 100. That is, if the laser beam scanable range is R2, the effective scanning range is R1, and the image formation start position is X as shown in the figure, the beam detection means 106 and 107 are within the range of R2, and the image formation start position X Placed in front of. In this embodiment, as will be described later, two detection means 106 and 107 are arranged side by side in the sub-scanning direction.

  The beam detection means 106 and 107 include two photodiodes (hereinafter referred to as PD1 and PD2) that photoelectrically convert a laser beam. In this embodiment, a photo IC 108 is formed by PD1, PD2, and a conversion circuit. Although details of the conversion circuit are omitted, the outputs PD1OUT and PD2OUT of PD1 and PD2 are compared, and an on and off digital signal is generated according to the comparison result. FIG. 3 is a schematic diagram of the photo IC 108.

  Now, as shown in FIG. 4, when two laser beams, for example, S1 and S3, are scanned on the PD1 and PD2 formed on the beam detecting means 106 or 107, first, the first laser beam S1 passes PD1. PD1 is turned on only during the irradiation time, and PD1 is turned off when the laser beam stops irradiating PD1. Similarly, when the laser beam S1 irradiates PD2, PD2 is turned on, and when the laser beam no longer irradiates PD2PD2, PD2 is turned off. Subsequently, the second laser beam S3 is irradiated and the same operation is performed. The conversion circuit in the photo IC 108 compares PD1OUT and PD2OUT, for example, outputs an L (low) level detection signal when PD1OUT> PD2OUT, and conversely outputs an H (high) level detection signal when PD2OUT> PD1OUT. Operates to output.

  FIG. 5A shows a waveform diagram of a detection signal obtained from the photo IC 108. The first pulse represents a signal generated when the laser beam S1 scans PD1 and PD2, and the second pulse It represents a signal generated when the laser beam S3 scans PD1 and PD2. These detection signals are applied to the control unit 120 in FIG. As shown in FIG. 5B, the control unit 120 generates image data of the first beam with a predetermined distance L or a predetermined time T after the first pulse as an image formation start position. As described above, the LDA 101 and the LDA 102 are controlled so as to generate the image data of the second beam with the predetermined distance L or the predetermined time T from the second pulse as the image formation start position.

  In this embodiment, as shown in FIG. 2, the light spots of laser beams S1 and S2, S3 and S4,... S9 and S10 are imaged so that the positions in the main scanning line direction are aligned. One beam detection means cannot detect these laser beam pairs.

  For this reason, in the first embodiment of the present invention, as shown in FIG. 6, two beam detecting means 106 and 107 are used, which are arranged in the sub-scanning direction at substantially the same position in the main scanning direction. Made the configuration. At the time of beam detection, the deflection means 111 scans the beam detection means 106 for the laser beams S1, S3, S5, S7, and S9, and scans the beam detection means 107 for the laser beams S2, S4, S6, S8, and S10. did.

  That is, when the deflecting means 111 such as a prism or a galvano mirror is arranged in the optical path between the LDA 102 and the beam splitter 103 in FIG. 1 and each of the laser beams is detected by the beam detecting means 106 and 107, the apex angle of the prism Further, by adjusting the reflection surface angle of the galvanometer mirror, the optical path of the laser beam of the LDA 102 is changed as shown in FIG. In this embodiment, the laser beams S1, S3, S5, S7, and S9 of the LDA 101 pass through the beam detecting means 106, and the optical paths of the laser beams S2, S4, S6, S8, and S10 of the LDA 102 are changed by the deflecting means 111, It is configured to pass through the upper surface of the beam detection means 107. As a result, all the laser beams can be detected. After the beam detection, the deflecting unit 111 returns the laser beam to the positional relationship shown in FIG. 2, and the image formation start position is controlled based on the beam detection signal.

  According to the embodiment described above, the scanning with the laser beams S1 to S10 is performed as shown in FIG. 8, so that the effective scanning range R1 can be widened compared to the conventional case.

(Example 2)
FIGS. 9 and 10 show a second embodiment of the present invention. In order to prevent the effective scanning range from being narrowed, the beam detection means 106 and 107 are shifted by a slight distance L1 in the main scanning direction and arranged in the sub scanning direction. It is arranged. At the time of beam detection, a cylindrical lens 110 is arranged in the optical path between the fθ lens 105 and the beam detection means 106 and 107. When the cylindrical lens 110 is inserted, the shape of the laser beam becomes a vertically long beam S10, S20, S30... As shown in FIG.

  In FIG. 9, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 1, the deflecting means 111 is arranged in the optical path for guiding the light beam from the second semiconductor laser array (LDA) 102 to the beam splitter 103. However, in the embodiment of FIG. 9, it is not necessary to deflect the light beam. A reflection mirror 109 is used.

  Next, the operation of the control unit 120 will be described with reference to FIG. In the figure, (b) to (f) show the light emission timing of the LDA 101, and (a) shows the detection signal waveform of the beam detection means 106. Further, (h) to (i) show the light emission timing of the LDA 102, and (g) shows the detection signal waveform of the beam detection means 107.

  First, as shown in (b), the LDA 101 is caused to emit light for a predetermined time in consideration of the timing when the laser beam of the LDA 101 passes through the beam detecting means 106. The light emitted from the LDA 101 is converted into a vertically long spot as shown in S10 of FIG. 11 by the cylindrical lens 110 and passes through the beam detecting means 106. When the first laser beam S10 passes through the beam detecting means 106, the first pulse signal shown in FIG. Thereafter, the first laser beam S10 is extinguished, and no light is emitted at the timing when it passes through the beam detecting means 107. Therefore, no detection signal is generated from the detecting means 107.

  On the other hand, the LDA 102 is turned off while the laser beam S20 generated by the LDA 102 passes through the beam detecting means 106, as shown in FIG. As a result, the beam detection means 107 generates a detection signal such as the first pulse in FIG. Next, the LDA 101 emits light for a predetermined time as shown in FIG. When the third beam passes through the beam detection means 106, a detection signal such as a second pulse in FIG.

  The third beam is turned off when it passes through the beam detecting means 106 and turned off when it passes through the beam detecting means 107.

  Similarly, the LDA 102 emits light for a predetermined time at the timing shown in FIG. This timing is extinguished when passing through the beam detecting means 106, and light is emitted when passing through the beam detecting means 107, so that the detection signal such as the second pulse in FIG. Will occur.

  Similarly, the LDA 101 emits light as shown in (d), (e), and (f) of the figure, and the LDA 102 emits light at timings as shown in (j), (h), and (l) of the figure. As a result, a detection signal as shown in FIG. 5A is generated from the beam detection means 106, and a detection signal as shown in FIG. 5G is generated from the beam detection means 107, and the beam detection means for all laser beams. Is done.

  The control unit 120 determines the image formation start position based on the beam detection means by the beam detection means 106 and 107. That is, assuming that the image start position of the image data by the LDA 101 is set at a time interval L from the synchronization detection signal of the detection means 106, the image start position of the image data by the LDA 102 is calculated from the synchronization detection signal of the detection means 107 (L− The timing is set at a time interval of L1).

  After the beam detection, the cylindrical lens 110 is removed. For this reason, the positional relationship between the laser beams formed by the LDA 101 and the LDA 102 is as shown in FIG.

1 is a schematic configuration diagram illustrating a first embodiment of a main part of a multi-beam image forming apparatus according to the present invention. It is explanatory drawing which shows the positional relationship of the multi-beam formed by this invention apparatus. It is explanatory drawing of photo IC used for this invention apparatus. It is operation | movement explanatory drawing of the beam detection means used for this invention apparatus. It is explanatory drawing explaining the timing of the image formation start position in this invention. It is explanatory drawing which shows one Example of arrangement | positioning of the beam detection means in this invention. It is explanatory drawing which shows one Example of the system which detects the multi-beam of the positional relationship shown in FIG. It is explanatory drawing which shows the effective scanning range of the multi-beam in this invention. FIG. 5 is a schematic configuration diagram illustrating a second embodiment of the main part of the multi-beam image forming apparatus according to the present invention. It is explanatory drawing which shows the other Example of arrangement | positioning of the beam detection means in this invention. It is explanatory drawing explaining operation | movement of the 2nd Example of this invention apparatus. It is each part waveform diagram explaining operation | movement of 2nd Example of this invention apparatus. It is a schematic block diagram of the principal part of the conventional multibeam image forming apparatus. It is explanatory drawing of the synchronous signal detection part of a conventional apparatus. It is operation | movement explanatory drawing of the synchronizing signal detection part of a conventional apparatus. It is explanatory drawing which shows the positional relationship of the multi-beam formed with the conventional apparatus. It is explanatory drawing which shows the effective scanning range of the multi-beam in a conventional apparatus.

Explanation of symbols

100: Photosensitive drums 101, 102: Semiconductor laser array 103: Beam splitter 104: Polygon mirror 105: fθ lens 106, 107: Beam detection means 108: Photo IC
109: Reflection mirror 110: Cylindrical lens 111: Deflection means

Claims (5)

  First and second semiconductor laser arrays each composed of n (n is an arbitrary integer of 2 or more) laser elements and laser beams generated by the first and second semiconductor laser arrays are combined to produce 2n Multi-beam generating means for generating a laser beam, scanning means for scanning 2n laser beams generated by the multi-beam generating means, and a beam for generating a synchronization detection signal for synchronizing the scanning of each laser beam In a multi-beam image forming apparatus comprising a multi-beam scanning device having a detecting means, the beam detecting means is arranged at approximately the same position in the main scanning direction of the laser beam to be scanned and arranged in the sub-scanning direction. The first and second beam detecting means comprise n laser beams of the first semiconductor laser array by the first beam detecting means. And detecting the n number of laser beams of the second semiconductor laser array by the second beam detecting means, and based on detection signals from the first and second beam detecting means. A multi-beam image forming apparatus comprising a control unit that controls an image formation start position of 2n multi-beams.   First and second semiconductor laser arrays each composed of n (n is an arbitrary integer of 2 or more) laser elements and laser beams generated by the first and second semiconductor laser arrays are combined to produce 2n Multi-beam generating means for generating a laser beam, scanning means for scanning 2n laser beams generated by the multi-beam generating means, and a beam for generating a synchronization detection signal for synchronizing the scanning of each laser beam In a multi-beam image forming apparatus comprising a multi-beam scanning device having a detecting means, the beam detecting means is a position shifted by a predetermined interval L1 in the main scanning direction of the laser beam to be scanned and in the sub-scanning direction. The first and second beam detecting means are arranged side by side, and the first semiconductor laser array is formed by the first beam detecting means. Beam detection of two laser beams is performed, and beam detection means for n laser beams of the second semiconductor laser array is detected by the second beam detection means, from the first and second beam detection means. A multi-beam image forming apparatus comprising: a control unit that controls an image formation start position of 2n multi-beams based on a detection signal.   3. The multi-beam generating means according to claim 1, wherein the laser beam generated from the second semiconductor laser array at the time of beam detection of n laser beams generated from the second semiconductor laser array A multi-beam image forming apparatus comprising deflection means for deflecting an optical path of a beam so as to pass over the beam detection means.   3. The optical element according to claim 2, wherein an optical element is inserted between the scanning means and the beam detecting means at the time of beam detection, and the optical element generates a laser beam generated by the first and second semiconductor laser arrays. A multi-beam image forming apparatus, wherein the multi-beam image forming apparatus is deformed into a shape passing through both of the second beam detecting means. 5. The control unit according to claim 4, wherein the control unit turns off when the laser beam generated from the first semiconductor laser array passes through the second beam detecting means, and the laser beam generated from the second semiconductor laser array is the first. The multi-beam image forming apparatus is controlled so as to be turned off when passing through the beam detecting means.

Images